The invention relates to new improved double-metal cyanide (DMC) catalysts for the preparation of polyether-polyols by polyaddition of alkylene oxides on to starter compounds containing active hydrogen atoms.
Double-metal cyanide (DMC) catalysts for polyaddition of alkylene oxides on to starter compounds containing active hydrogen atoms are known (see, for example, U.S. Pat. Nos. 3,404,109, 3,829,505, 3,941,849 and 5,158,922). The use of these DMC catalysts for the preparation of polyether-polyols has the effect, in particular, of a reduction in the proportion of monofunctional polyethers with terminal double bonds, so-called monools, compared with the conventional preparation of polyether-polyols by means of alkali catalysts, such as alkali metal hydroxides. The polyether-polyols thus obtained can be processed to high-grade polyurethanes (e.g. elastomers, foams, coatings). DMC catalysts are usually obtained by reacting an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt in the presence of a low molecular weight organic complexing ligand, e.g. an ether. In a typical catalyst preparation, for example, aqueous solutions of zinc chloride (in excess) and potassium hexacyanocobaltate are mixed, and dimethoxyethane (glyme) is then added to the suspension formed. After filtration and washing of the catalyst with aqueous glyme solution, an active catalyst of the general formula
Zn3[Co(CN)6]2xc2x7xZnCl2xc2x7yH2Oxc2x7zglyme
is obtained (see e.g. EP 700 949).
JP 4 145 123, U.S. Pat. No. 5,470,813, EP 700 949, EP 743 093 and EP 761 708 disclose improved DMC catalysts which, by the use of tert-butanol as the organic complexing ligand (by itself or in combination with a polyether (EP 700 949, EP 761 708)), are capable of further reducing the proportion of monofunctional polyethers with terminal double bonds in the preparation of polyether-polyols. Furthermore, by using the improved DMC catalysts, the induction time for the polyaddition reaction of the alkylene oxides on to corresponding starter compounds is reduced and the catalyst activity is increased.
The object of the present invention is thus to provide DMC catalysts for the polyaddition of alkylene oxides on to corresponding starter compounds which are improved further and which have an induction time which is reduced considerably with respect to the catalyst types known to date, and at the same time a significantly increased catalyst activity. By shortening the total reaction and cycle times of the polyether-polyol preparation, this leads to an improved profitability of the process. Ideally, because of the increased activity, the catalyst can then be employed in such low concentrations that removal of the catalyst, which is otherwise very expensive, is no longer necessary, and the product can be used directly for polyurethane applications. Surprisingly, it has now been found that DMC catalysts which contain 5-80 wt. %, based on the amount of finished catalyst, of a polyester have significantly shortened induction times and at the same time a greatly increased activity in polyether-polyol preparation.